Maize 16-kD γ-zein forms very unusual disulfide-bonded polymers in the endoplasmic reticulum: implications for prolamin evolution

Mainieri, Davide; Marrano, Claudia Adriana; Prinsi, Bhakti; Maffi, D.; Tschofen, Marc; Espen, Luca; Stöger, Eva; Faoro, Franco; Vitale, Alessandro

doi:10.1093/jxb/ery287

Cited by 17 publications

(24 citation statements)

References 58 publications

(107 reference statements)

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“…For instance, maize Mucronate mutation forms a misfolded 16-kDa γ-zein that leads to irregular PB formation, but it could be rescued to restore normal PB by silencing the expression of the mutant 16-kDa γ-zein gene (34,35). Although 16-kDa γ-zein lost a large part of its N-terminal domain compared with 27-kDa γ-zein that was able to promote PB formation (36,37), a recent study showed that 16-kDa γ-zein acquired a new function in PB assembly (38). Furthermore, the 16-kDa γ-zein promoter lost all known conserved cis-elements present in other zein promoters (5) but acquired the cis-element ACGCAA, recognized by the corresponding NAC TFs, thereby restoring its endosperm-specific expression and synchronization with starch storage.…”

Section: Discussionmentioning

confidence: 99%

NAC-type transcription factors regulate accumulation of starch and protein in maize seeds

Zhang

Dong

Chen

et al. 2019

Proc. Natl. Acad. Sci. U.S.A.

129

126

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Grain starch and protein are synthesized during endosperm development, prompting the question of what regulatory mechanism underlies the synchronization of the accumulation of secondary and primary gene products. We found that two endosperm-specific NAC transcription factors, ZmNAC128 and ZmNAC130, have such a regulatory function. Knockdown of expression of ZmNAC128 and ZmNAC130 with RNA interference (RNAi) caused a shrunken kernel phenotype with significant reduction of starch and protein. We could show that ZmNAC128 and ZmNAC130 regulate the transcription of Bt2 and then reduce its protein level, a rate-limiting step in starch synthesis of maize endosperm. Lack of ZmNAC128 and ZmNAC130 also reduced accumulation of zeins and nonzeins by 18% and 24% compared with nontransgenic siblings, respectively. Although ZmNAC128 and ZmNAC130 affected expression of zein genes in general, they specifically activated transcription of the 16-kDa γ-zein gene. The two transcription factors did not dimerize with each other but exemplified redundancy, whereas individual discovery of their function was not amenable to conventional genetics but illustrated the power of RNAi. Given that both the Bt2 and the 16-kDa γ-zein genes were activated by ZmNAC128 or ZmNAC130, we could identify a core binding site ACGCAA contained within their target promoter regions by combining Dual-Luciferase Reporter and Electrophoretic Mobility Shift assays. Consistent with these properties, transcriptomic profiling uncovered that lack of ZmNAC128 and ZmNAC130 had a pleiotropic effect on the utilization of carbohydrates and amino acids. maize endosperm | gene regulation | starch synthesis | protein

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Section: Discussionmentioning

confidence: 99%

NAC-type transcription factors regulate accumulation of starch and protein in maize seeds

Zhang

Dong

Chen

et al. 2019

Proc. Natl. Acad. Sci. U.S.A.

129

126

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“…The increased prolamin yield in Method 2 (average 0.79 g/100 g flour) from Method 1 (0.09) indicate that teff prolamines are prone to oxidative damage and can be effectively protected by reducing agents during extraction. This protein fraction has been reported to form disulfide bonds during extraction and reducing agents effectively enhanced their extraction yield by preventing the formation of disulfide bonds [33]. Here, it can be assumed that the increase in prolamin yield is due to an increase in overall solubility and a decrease in the oxidation damage of the fraction.…”

Section: Discussionmentioning

confidence: 99%

Variations in Amino Acid and Protein Profiles in White versus Brown Teff (Eragrostis Tef) Seeds, and Effect of Extraction Methods on Protein Yields

Gebru

Hyun-Ii

Kim

et al. 2019

Foods

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Data on variations in amino acid compositions and protein profiles among white and brown teff, a grain of growing interest, is either limited or contradicting at the moment. In this study, three white (Addis-W, Mekel-W and Debre-W) and three brown (Addis-B, Mekel-B and Debre-B) teff seed samples were used for whole flour amino acid analysis and protein fractionation with three different methods. White and brown seed types showed different physical changes during protein extraction. Brown teff displayed higher essential amino acid content than white with lysine present in high concentration in both seed types. Extraction with tert-butanol increased prolamin yields in teff compared to ethanol. The major protein fraction in teff was glutelin with white teff containing higher glutelin proportion than brown. Sodium Dodecyl Sulfate Gel Electrophoresis (SDS-PAGE) analysis revealed clear genetic variability between white and brown teff seed types.

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“…Alpha and delta zeins constitute the core of the PB, whereas 27 kDa and 50 kDa gamma zeins (27γz, 50γz) form the outer PB layer, in contact with the luminal face of the ER membrane, and 16 kDa gamma zein (16γz) is at the interface between the inner core and outer PB layer [ 2 , 12 ]. 27γz, the single most abundant PB polypeptide, forms homotypic, insoluble, electron-dense PBs also when ectopically expressed in vegetative tissues [ 13 , 14 ]. Unlike α-zeins, which can be solubilized by aqueous alcohol, 27γz and 50γz are solubilized by reducing buffers; in agreement with this, progressive mutagenesis of the Cys residues involved in the interchain bonds of 27γz results in its increasing solubility and ability to traffic from the ER along the secretory pathway [ 15 ].…”

Section: Introductionmentioning

confidence: 99%

Progressive Aggregation of 16 kDa Gamma-Zein during Seed Maturation in Transgenic Arabidopsis thaliana

Arcalís

Mainieri

Vitale

et al. 2021

IJMS

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Prolamins constitute a unique class of seed storage proteins, present only in grasses. In the lumen of the endoplasmic reticulum (ER), prolamins form large, insoluble heteropolymers termed protein bodies (PB). In transgenic Arabidopsis (Arabidopsis thaliana) leaves, the major maize (Zea mays) prolamin, 27 kDa γ-zein (27γz), assembles into insoluble disulfide-linked polymers, as in maize endosperm, forming homotypic PB. The 16 kDa γ-zein (16γz), evolved from 27γz, instead forms disulfide-bonded dispersed electron-dense threads that enlarge the ER lumen without assembling into PB. We have investigated whether the peculiar features of 16γz are also maintained during transgenic seed development. We show that 16γz progressively changes its electron microscopy appearance during transgenic Arabidopsis embryo maturation, from dispersed threads to PB-like, compact structures. In mature seeds, 16γz and 27γz PBs appear very similar. However, when mature embryos are treated with a reducing agent, 27γz is fully solubilized, as expected, whereas 16γz remains largely insoluble also in reducing conditions and drives insolubilization of the ER chaperone BiP. These results indicate that 16γz expressed in the absence of the other zein partners forms aggregates in a storage tissue, strongly supporting the view that 16γz behaves as the unassembled subunit of a large heteropolymer, the PB, and could have evolved successfully only following the emergence of the much more structurally self-sufficient 27γz.

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Maize 16-kD γ-zein forms very unusual disulfide-bonded polymers in the endoplasmic reticulum: implications for prolamin evolution

Abstract: A prolamin paralog generated upon maize whole-genome duplication has changed its polymerization and solubility properties, allowing a new function in the assembly of maize protein bodies.

Cited by 17 publications

References 58 publications

NAC-type transcription factors regulate accumulation of starch and protein in maize seeds

NAC-type transcription factors regulate accumulation of starch and protein in maize seeds

Variations in Amino Acid and Protein Profiles in White versus Brown Teff (Eragrostis Tef) Seeds, and Effect of Extraction Methods on Protein Yields

Progressive Aggregation of 16 kDa Gamma-Zein during Seed Maturation in Transgenic Arabidopsis thaliana

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